RIYADH - Saudi Arabia's Grand Mufti urged young people on Thursday to ignore calls to jihad from people representing "deviant principles", the latest salvo in an anti-militant campaign by the kingdom's religious establishment.

Riyadh, the world's No. 1 oil exporter, is unnerved by the rapid advance in Iraq and Syria of Islamic State insurgents and fears this could radicalize some of its own citizens and eventually lead to attacks on the US-allied government.

The word "deviant" is usually used in official and religious Saudi circles to refer to the Islamist militant ideology followed by al-Qaida, of which Islamic State is an offshoot.

Sheikh Abdulaziz Al al-Sheikh, the highest religious authority in the country, this month described the creed of al-Qaida and Islamic State as Islam's "enemy number one", a message echoed in Friday sermons across the country.

Riyadh is among the main backers of mostly Sunni Muslim rebels, although not Islamic State, fighting President Bashar Assad of Syria. While Saudi clergy have backed the rebels' campaign as a jihad on the part of the Syrian people, they have said it is not a jihad for Saudis.